The commission is charged with fixing mental healthcare in NSW and has the power to compel other public sector agencies to co-operate with it.

The Greens will move to amend the legislation after the NSW Parliament returns tomorrow.

Megan Mitchell, who heads the Commission for Children and Young People, has written to the parliamentary committee that overseas her statutory authority to express her concerns.

She said the government legislation establishing the Mental Health Commission "fails to identify children and young people as a group whose particular views and needs the Mental Health Commission must take into account in exercising its functions".

"This is despite the fact that the needs of other groups in the community is specifically identified," she said. "I consider this a significant failing of the current bill."

Section 12 of the bill requires the Mental Health Commission to take into account the views and needs of Aboriginal and "culturally and linguistically diverse" communities along with those in regional and remote areas.

Greens NSW MP John Kaye said the legislation overlooked one of the "most prevalent and vulnerable groups".

He said the Greens would move to amend the legislation to include the specific needs of children and young people.

"The O'Farrell government has been hauled over the coals by its own youth watchdog for ignoring the specific mental health needs of young people," Dr Kaye said.

"Mental Health Minister Kevin Humphries has damaged the credibility of his consultation process by ignoring the advice of Children and Young People Commissioner Megan Mitchell.

"She has now taken the extraordinary step of airing her concerns to MPs. This time the minister should listen."

A spokesman for Mr Humphries said the government was committed to establishing the Mental Health Commission "based on best practice".

A commission taskforce has been seeking community views including those of child and adolescent mental health groups and specialists since June last year.

"The needs of children and adolescents are critical for the commission to consider," the spokesman said.

"However, it is important to remember that, in drafting legislation, we should not attempt to list exhaustively groups, as to do so may unintentionally limit scope.

"We would expect the commission in undertaking its functions to consider the needs of the full range of the population and age groups, including of course the needs of children and adolescents, as well as their families and carers."